irm-EAMS (δ13C and δ15N)
CO2 in-air (δ13C and δ18O)
O2/N2 in air (+ δ18O of O2 in air or Ar/N2)
Laser Ablation
GasBench
TC/EA ('Pyrolysis', δ2H and δ18O)
Acid reaction and air mixing system (ARAMIS) (δ13C and δ18O)
Acid reaction and air mixing system (ARAMIS) (δ13C and δ18O) In order to generate a reliable and long lasting stable isotope ratio standard for CO2 in samples of clean air, CO2 is liberated from well characterized carbonate material and mixed with CO2-free air. For this purpose a dedicated acid reaction and air mixing system (ARAMIS) was designed. In the system, CO2 is generated by the conventional acid digestion of powdered carbonate.
CaCO3 + 2 H3PO4 ---> Ca(H2PO4)2 + CO2 + H2O
Evolved CO2 gas is mixed and equilibrated with a prefabricated gas comprised of N2, O2, Ar, and N2O at close to ambient air concentrations. Distribution into glass flasks is made stepwise in a highly controlled fashion. The isotopic composition, established on automated extraction / measurement systems, varied within very small margins of error appropriate for high precision air-CO2 work (about ± 0.015 ‰ for δ13C and ± 0.025 ‰ for δ18O). For establishing a valid δ18O relation to the VPDB scale, the temperature dependence of the reaction between 25°C and 47°C has been determined with a high level of precision.
Using identical procedures, CO2-in-air mixtures were generated from a selection of reference materials; (1) the material defining the VPDB isotope scale (NBS 19, δ13C = +1.95 ‰ and δ18O = -2.2 ‰ exactly); (2) a local calcite similar in isotopic composition to NBS 19 (‘MAR-J1’, δ13C = +1.97 ‰ and δ18O = -2.02 ‰), and (3) a natural calcite with isotopic compositions closer to atmospheric values (‘OMC-J1’, δ13C = -4.24 ‰ and δ18O = -8.71 ‰)
As a result of the experiments, a new standard reference material (SRM), which consists of two 5-L glass flasks containing air at 1.6 bar and the CO2 evolved from two different carbonate materials, is available for distribution. These ‘J-RAS’ SRM flasks
‘Jena-Reference Air Set’
are designed to serve as a high precision link to VPDB for improving inter-laboratory comparability.
More information can be found in:
Prosenjit Ghosh, Michael Patecki, Michael Rothe, and Willi A. Brand, Calcite-CO2 Mixed into CO2-free Air: A New CO2‑in-Air Stable Isotope Reference Material for the VPDB Scale, Rapid Comm. Mass Spectrom., (2005), 19: 1097-1119 W. A. Brand, M. Rothe, J. Richter, Relating Air-CO2 Isotope Ratio Determinations to VPDB using Calcite-CO2 Mixed into CO2-free Air, Proceedings of the 13th IAEA/WMO meeting of CO2 experts, Boulder, Sept. 2005, WMO-GAW Report 168, ed. J.B. Miller (2007), 36-40 http://www.wmo.int/pages/prog/arep/gaw/gaw-reports.html)
Laboratory carbonate reference materials were prepared from a (limestone) marble slab (‘MAR-J1’, Marble-Jena #1) purchased from a local vendor and from a calcite slab from the Meieberg section of the Otavi platform in northern Namibia[i] (‘OMC-J1’; Otavi Meieberg Calcite-Jena #1), which was kindly provided by Paul Hoffmann. The slabs were broken into chips, crushed into fine grains, and sieved into fractions.
MAR-J1: 13C: 1.97 ‰; 18O: -2.02 ‰ VPDB The <250 µ size fractions weighing about 900 g was labeled ‘MAR-J1’. Texture and appearance of the powder is similar to NBS 19 carbonate material. Other fractions, 250-315 µ (~500 g) and 315-400 µ (~300 g), were designated as ‘MAR-J2’ and ‘MAR-J3’ and stored for future use. Quantitative analysis using ICP-MS and ICP-OES indicated an average CaCO3 content of 98.0 % and 2.0 % MgCO3. Al, Fe, Cu, Mn, Na, K together were less than 0.1 %. NBS 19 (TS limestone) is very similar: in line with literature XRF data[ii] we obtained 98.1 % CaCO3 and 1.8 % MgCO3. Other elements were 0.08 % in total. The similarity of the two materials is further confirmed by observing the carbonate reaction yield with NBS 19 and MAR-J1 resulting in the same amounts of CO2 gas.
OMC-J1: 13C: -4.4 ‰; 18O: -8.4 ‰ VPDB (final batch, not 1st drill) The composition analysis of the Otavi-Meieberg calcite using ICP-AES and ICP-OES has given 98.7 % CaCO3 and 0.9 % MgCO3 with non-carbonate cationic impurities summing up to 0.4 %. The crushing, milling and sieving left us with 1270 g powder with a grain size <100 µ (‘OMC-J0’), 700 g between 100 and 200 µ (‘OMC-J1’) and 1800g between 200 and 400 µ (‘OMC-J2/3’). In order to avoid oxygen exchange with ambient moisture or CO2 all fractions are kept in glass or PE jars topped with Ar.